The present invention relates to a multiple beam spacer and, more particularly, to a single refractive optical element and a segmented mirror which control the separation between four parallel laser beams.
Printing systems will use a raster output scanning (ROS) system to have a modulated light beam strike the facets of a rotating polygon mirror and scan in a raster pattern across a photoreceptor. High speed or color printing requires a multiple beam light source.
One possible multiple beam light source is a lager diode array. However, placing two or more laser diodes in a single array creates practical difficulties including phase locking of the emitted laser beams and electrical and thermal interference between the adjacent laser beams.
Another approach to providing a multiple beam light source is to integrate individual lager diodes to form the multiple light beam source. In a ROS system, it is beneficial to have the rotating polygon as thin as possible. Thicker polygons cost more and require larger, higher power and more expensive motors and drivers. A four parallel beam ROS therefore requires that the four beams be closely spaced in order to enable a thin polygon.
The major problem with integrating individual laser diodes into a multiple beam light source is the large spacing between the individual laser diodes caused by the physical size of the laser diodes themselves. The spacing or pitch between two adjacent individual laser diodes can be 100 microns or larger while the required spacing of the two adjacent light beams for printing uses is 25 microns or less, a difference of a factor of four or greater. Also multiple laser beam systems are often required to have beam to beam spacing that is considerably different in different parts of the system.
A beam spacer uses optical elements to expand or contract the pitch or spacing between light beams.
Current technology can use mirrors and lenses as beam spacers. However, manufacturing these optical elements on such a small micron scale requires expensive, extensive fabrication and align the various optical elements on an even smaller scale mandates a precision assembly.
Beam combiners, as their name indicates, are optical elements that combine two or more light beams into a single overlapping composite beam. These are distinctly different optical elements from beam spacers which move light beams closer without combining the beams.
Beam splitter prisms can be used as beam spacer elements, but this approach reduces the intensity of the output beam by half due to light loss caused by splitting the beam. A tilt plate and a pair of beam steering prisms (or a second tilt plate) are used to split a wide horizontal beam into two smaller vertically aligned beams in U.S. Pat. No. 5,557,475 to improve the brightness symmetry of the beam.
One possible beam spacer is found in U.S. Pat. No. 5,566,024, commonly assigned as the present application and herein incorporated by reference. Two sets of two single blazed binary diffractive optical elements form a beam spacer for contracting two wider spaced parallel beams into two closely spaced parallel beams.
It is an object of the present invention to provide a multiple beam separation spacer of a single refractive optical element and a segmented mirror which control the spacing between four parallel laser beams.
According to the present invention, a segmented mirror with alternating reflective and transmissive surfaces and a refractive tilt place which laterally displaces two parallel beams are used as a beam spacer.
A first beam is reflected by the segmented mirror and a second beam is transmitted by the segmented mirror. A third beam is refracted and laterally displaced by the tilt plate then reflected by the segmented mirror while a fourth beam is beam is refracted and laterally displaced by the tilt plate then transmitted by the segmented mirror. The segmented mirror and the refractive tilt plate closely space four parallel laser beams.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.